1. Field of the Invention
The instant disclosure relates to a light-guiding plate and a backlight module, and more particularly, to a light-guiding plate and a backlight module for increasing the light-guiding efficiency and the light usage rate of the positive light source.
2. Description of Related Art
Among all kinds of flat display devices, a liquid crystal display (LCD) device with low electrical power consumption, low voltage operation, thinner thickness and lighter weight, is widely used in nowadays. A liquid crystal display device typically includes a first substrate having common electrodes and a color filter, and a second substrate having thin film transistors and pixel electrodes. The first substrate and the second substrate are provided substantially in parallel with a predetermined gap therebetween, and liquid crystal is injected between the two opposing substrates. An electric field is formed between the substrates by applying different voltages to the pixel electrodes and common electrodes. Accordingly, the alignment of liquid crystal molecules of the liquid crystal material is varied to thereby control the transmittance of incident light. The visions of liquid crystal display devices are extremely excellent since the displayed figures or pictures are not offensive to the eyes of human being unlike light emitting diode. But it is one of the drawbacks of LCD that an additional light module is needed in order to show figures or pictures on the screen under the dark circumstance because LCD does not have the character of light-emitting itself.
In the prior art, U.S. Pat. No. 5,838,403 discloses a backlight module using at least two light-guiding plates and at least one light-converging sheet mated with each other. In general, the light-projecting direction of the light source can be adjusted by the prism structures formed on the bottom portion of the light-guiding plate. However, the light usage rate of the positive light source can not be effectively increased by using the prism structures, where the positive light source is a projection light substantially vertical to the light-guiding plate.